A pigment suspension generally comprises a solvent, usually water, pigments and, optionally, a plasticiser for reducing the viscosity and/or increasing the pigment concentration thereof.
The color strength is an essential property of pigment compositions. It defines the amount of pigment composition necessary to obtain a desired color shade.
For the majority of applications it is preferred to have a pigment suspension with a high color strength. Not only does this represent an economic factor; the material added to the composition to be colored is also limited. The latter factor is particularly important for hydraulically setting materials, the optimized formulation of which can be very sensitive to the presence of ions.
US patent application 2007/0022914 proposes adding partially or fully hydrolysed polyvinyl alcohols or sulfur- or phosphorus-containing compounds to pigment suspensions in order to improve the color strength thereof.
Such compounds are not satisfactory, however.
Patent application EP 0 567 214 describes the use of a copolymer obtained by polymerization of methacrylic acid, methacrylates and styrene as a pigment dispersing agent.
However, such compounds can sometimes pose problems owing to their residual monomer content. In addition, the hydrophobic nature limits their absorption at the surface of the polar pigment particles and accordingly their dispersion capacity.